1
1° emerge aspell aspell-fr 2° set-up spell checking in control center to use aspell [1] 3° launch a kde application (kate, kedit,...) and try to use the spell checker: "aspell could not be starded Please make sure you have aspell properly configured and in your PATH." 4° emerge aspell-en 5° retry step 3° and it works! My KDE is configured in french in the control center and aspell and aspell-fr are installed, spell checking in KDE apps should not require aspell-en to work. Maybe "ASpell default" is "English" but then, control center should provide a way to select installed languages. I don't have the choice to use something other than "ASpell default" [1] Dictionnary: ASpell default, Encoding: UTF-8, Client: Aspell Don't think my emerge --info is interesting, if you need it, just ask me
Testing the spell checkers I ran into nice crashes but your problem is not reroducible for me using e.g. aspell-de or aspell-de and aspell-fr. Having solely aspell-fr installed I can reproduce your problem. As this is a problem with aspell-da and probably others, too, I'll add aspell-en as dependency, but please don't miss to report the problem at https://bugs.kde.org as it needs to be fixed there.
The aspell-en dependencies was the reason for an aspell block I got during emerge -uvD world. The aspell-en wanted the old aspell-0.5* and didn't fit to the aspell-0.6. After I removed the aspell-en dependency in the ebuild everything worked fine again. So you traded one problem for another ;-)